Specificity in the interaction of direct dyes with polysaccharides

A number of polysaccharides have been shown to interact in solution with the direct dyes Calcofluor White M2R New (Calcofluor) and Congo Red. Complex formation was detected by changes in solubility and in the fluorescence and absorption spectra of the dyes. Strongest interaction, as evidenced by precipitation, bathochromic shifts >20 nm with Congo Red and >10 nm with Calcofluor, and a major (4–7 fold) increase in fluorescence intensity, was shown by polysaccharides known to contain contiguous (1→4)-β-linked d-glucopyranosyl units. such as cereal β-d-glucans, xyloglucan, and substituted celluloses. Evidence of complex formation was also shown by some other polysaccharides, such as (1→3)-β-d-glucan and hemicellulosic galactoglucomannans, but most polysaccharides showed little or no, interaction. The two dyes differed in their affinities for the different polysaccharides tested. Cellopentaose and higher, but not lower, oligomers showed interaction.